1. Field of the Invention
The present invention generally relates to selected phase change ink compositions containing certain polymeric dyes in combination with certain phase change ink carrier compositions.
2. Brief Description of the Related Art
In general, phase change inks are in the solid phase at ambient temperature, but exist in the liquid phase at the elevated operating temperature of an ink jet printing device. At the jet operating temperature, droplets of liquid ink are ejected from the printing device and, when the ink droplets contact the surface of the printing media, they quickly solidify to form a predetermined pattern of solidified ink drops.
Phase change inks are desirable for ink jet printers since they remain in a solid phase at room temperature, during shipping, long-term storage, and the like. Also, the problems associated with nozzle clogging due to ink evaporation are largely eliminated, thereby improving the reliability of ink jet printing. Furthermore, in prior art phase change ink jet printers where the ink droplets solidify immediately upon contact with the substrate, migration of ink along the printing medium is prevented and dot quality is improved. This is also true of the processes and ink compositions described herein.
The phase change inks generally comprise a phase change ink carrier composition that is combined with a phase change ink compatible colorant. Preferably, a colored phase change ink will be formed by combining the above-described ink carrier composition with compatible subtractive primary colorants. The subtractive primary colored phase change inks of this invention comprise four component dyes, namely, cyan, magenta, yellow and black. U.S. Pat. Nos. 4,889,560 and 5,372,852 teach the subtractive primary colorants employed typically may comprise dyes from the classes of Color Index (C.I.) Solvent Dyes, Disperse Dyes, modified Acid and Direct Dyes, and a limited number Basic Dyes.
U.S. Pat. No. 5,621,022 teaches the use of certain polymeric dyes in a phase change ink composition. These polymeric dyes were selected from the group consisting of (1) an organic chromophore having a polyoxalkylene substituent and (2) an organic chromophore having a polyoxyalkylene substituent and a carboxylic acid or nonreactive derivative thereof covalently bonded to the poly-oxyalkylene substituent. Examples of these polymeric dyes are available from Milliken & Company and include Milliken Ink Yellow 869, Milliken Ink Blue 92, Milliken Ink Red 357, Milliken Ink Yellow 1800, Milliken Ink Black 8915-67.
The use of these polymeric dyes in phase change inks were found to possess several unexpected results including:
(1) These polymeric dyes are very soluble in the phase change carrier composition and possess high water fastness and high resistance to "bleeding" or weeping of the color from the carrier composition when printed samples are subjected to high temperatures or humidity.
(2) These polymeric dyes are thermally stable in the carrier composition. This is important because the resulting phase change ink compositions may remain molten for weeks at a time in the ink jet printer.
(3) These polymeric dyes also act as a plasticizer for the formulation. This enables the formulator to replace at least a portion of the commercial plasticizer that is normally part of the formulations disclosed in the inks of U.S. Pat. Nos. 4,889,506 and 5,372,852.
(4) These polymeric dyes are compatible with each other and with most conventional powdered dyes currently used in phase change ink compositions. Thus, mixtures of inks of different colors do not form a precipitate when mixed together. This is important because, during the purging and wiping procedures that are used in maintenance of the ink jet device, all four colors of ink are mixed together on the faceplate of the jet array. Any precipitates caused by reactions between inks or dyes have the potential to clog the orifices of the jets. This compatibility also allows for the mixing of these polymeric dyes with powdered dyes of the same primary color into the same ink composition to achieve high color strengths that would not be possible with either dye type by itself.
Separately, U.S. Pat. No. 5,827,918, filed on Jun. 28, 1996 and assigned to the same assignee as the present application, discloses the use of urethane isocyanate-derived resins, urea isocyanate derived resin and monomide in the phase change ink carrier composition for a phase change ink. This patent also teaches that polymeric dyes such as those disclosed in U.S. Pat. No. 5,621,022 may be used as the phase change colorant materials. In particular, Example 16 of this U.S. patent discloses a yellow ink made from a urethane wax (reaction product of octadecyl alcohol and octadecylisocyanate), an urethane resin (reaction product of octylphenol ethoxylate and isophorone diisocyanate), a tackifier resin (glycerol ester of hydrogenated abietic (rosin) acid), an antioxidant and a yellow polymeric acid (Milliken Yellow 869). This patent did not teach that this particular yellow ink or any other ink described in this application possessed photochromic properties.
The photochromic effect (photochromism) in general is a reversible change of a single chemical species between two states having distinguishably different absorption spectra, wherein the change is induced in at least one direction by the action of electromagnetic radiation. This inducing radiation, as well as the changes in the absorption spectra, is usually in the ultra-violent, visible or infrared regions. In some instances, the change in one direction may also be thermally induced. The single chemical species can be a molecule or an ion, and the reversible change in states may be a conversion between two molecules or ions, or the dissociation of a single molecule or ion into two or more species, with the reverse change being a recombination of the two or more species thus formed into the original molecule or ion. Photochromic phenomena are observed in both organic compounds, such as anils, disulfoxides, hydrazones, osazones, semicarbazones, stilbene derivatives, o-nitrobenzyl derivatives, spiro compounds, and the like, and in inorganic compounds, such as metal oxides, alkaline earth metal sulfides, titanates, mercury compounds, copper compounds, minerals, transition metal compounds such as carbonyls, and the like. Inks containing photochromic components could be used as a security ink, watermark or to create some other means for authenticating a document (e.g., a stock certificate).
Accordingly, there is a need for new photochromic inks to act as new ways for authenticating documents or to provide a way to differentiate items from one another. The present invention provides a solution to that need.